Source: http://www.abarim-publications.com/Meaning/Philadelphia.html

🔼The name Philadelphia in the Bible

The name Philadelphia occurs only twice in the Bible, both times in Revelation, as Philadelphia is one of the seven cities of Asia Minor (in modern Turkey) to which Revelation was addressed (Revelation 1:11 and 3:7). Today this city is known as Alasehir (or Allah-Sheryr), meaning "city of God".

In New Testament times, Philadelphia was a relatively new city, having been founded in 189 BC by king Eumenes II and named for the love of his brother and successor Attalus I. In 17 AD the city was badly damaged in an earthquake, after which it was exempted from taxes.

Jesus' message to Philadelphia via John the Revelator is remarkably positive, albeit doubtlessly period-bound and therefore rather hard to understand for us moderns:

The "open door" of Revelation 3:8 is generally considered a mystery, but here at Abarim Publications we surmise it may refer to the war-doors of the temple of Janus Quirinus (see our article on the name Quirinius). These doors would be ceremoniously opened in times of war (and sometimes stay open for centuries on end) and be closed in times of peace. As Rome's territory grew, wars got larger and thus more costly, and peace got an increasingly better rep. During the reign of Caesar Augustus, peace and social stability, though wrought by means of hideous suppression and genocides, became deified as the goddess Pax, and the closing of the doors of Janus Quirinus was executed with increasing fanfare.

The reference to the "synagogue of satan" is also a bit obscure, although the satan of Revelation is obviously Rome (see Revelation 3:9, and also 2:9, 2:13 and 2:24). Before the Romans murdered everybody and turned the Celtic and Phoenician worlds into wastelands, humanity enjoyed a period of democracy and free trade based on mutual respect and voluntary contribution. Particularly when the Roman Republic became Empire, mankind entered into a nightmare that lasted well until the Renaissance, and still keeps most of us in a groggy slumber.

The "pillar in the temple of God" may refer to a strand of wisdom or skill — compare Revelation 1:14 to Proverbs 9:1, and Exodus 2:16 to Isaiah 4:1; and also see our article on the name Stoics for the importance of the word "pillar" in this regard.

It should be noted with some additional suspicion that in New Testament times, the name Philadelphia was probably much more prominently attached to the city now known as Amman, the capital city of Jordan and in Old Testament times as Rabbath-bene-ammon. This city was named such after its ruler, Ptolemy II Philadelphus (3rd century BC), and remained known as such until well in the Roman Christian era.

🔼Etymology of the name Philadelphia

The name Philadelphia is the same as the common noun φιλαδελφια (philadelphia), meaning brotherly love and which occurs five times in the New Testament (Romans 12:10, 1 Thessalonians 4:9, Hebrews 13:1, 1 Peter 1:22 and 2 Peter 1:7). This noun, and thus the name Philadelphia, consists of two elements:

The first part of our name comes from the familiar adjective φιλος (philos), meaning friend or beloved: